Polyurethane and polyisocyanurate foam insulation boards are commonly employed in the construction industry. These insulation boards are generally cellular in nature and typically include an insulating compound trapped within the cells of the foam.
The physical characteristics of the board are important to the overall performance of the board. For example, dimensional stability is important because insulation boards are exposed to a full range of weather. Where insulation boards are employed to insulate flat or low-slope roofs, shrinkage of these insulation boards from cold temperatures can cause a loss of insulating efficiency. In particular, when the dimensional stability of the foam matrix is low, the edges (especially the 8′ edges of, for example, standard 4′×8′ boards) are susceptible to edge collapse during exposure to cold temperatures. This collapse can cause the top facers and bottom facers along these edges to bend towards each other.
As a result, it is common in the industry to test insulation boards for cold-age dimensional stability (ASTM D2126). Alternatively, the dimensional stability of insulation boards, primarily the edges, can be determined by analyzing the perpendicular compressive strength of these edges (i.e. the compressive strength in the cross-machine direction). The higher the perpendicular compressive strength of the insulation boards along these edges, the better the cold age dimensional stability of the insulation boards.
The dimensional stability of insulation boards is believed to be impacted, especially near the edges of the board, by the degree of polyurethane crosslinking (isocyanurate formation). Incomplete crosslinking tends to be a problem near the edges of the board because less heat is present at the edges following manufacture of the boards. In other words, the boards are typically stacked or bundled following manufacture, and the heat that is generated and trapped within the boards tends to drive crosslinking; the exposed surface area around the edges of the stacks or bundles allows the edges to cool more rapidly which results in decreased crosslinking.
Also, the dimensional stability of insulation boards is believed to be impacted, especially near the edges of the board, by the shape and orientation of the cells within the foam. Particularly, it is believed that if the cells of the foam matrix are spherically-shaped, instead of being egg-shaped, then the dimensional stability of the roofing board is relatively high; but if the cells are egg-shaped, then the dimensional stability of the roofing board is relatively low along at least one of the three major axes. For example, if the major (as opposed to minor) axes of the egg-shaped cells are aligned parallel to the rise direction of the foam (i.e. perpendicular to the facers), then the dimensional stability perpendicular to the rise direction will be relatively low.
Several solutions have been suggested in the prior art and/or are practiced commercially to improve the dimensional stability of the insulation boards, particularly along edges. These solutions primarily involve adjusting manufacturing parameters. These parameters include, but are not limited to, manufacturing techniques, conditions, ingredients, and ingredient amounts. Thus, one could use compressive strength analysis to glean dimensional stability and alter these manufacturing parameters to produce an insulation board having a technologically useful dimensional stability.
But, the problem encountered derives from the fact that insulation boards are commercially produced in a continuous operation. These continuous manufacturing processes can suffer from quality control issues—particularly related to dimensional stability along the edges because adjustments to these processing parameters are best made during the process. Heretofore in the art, these adjustments to the processing parameters were made only after an insulation board was removed from the process, analyzed for compressive strength, and the data from this test was provided to an operator who could then make the appropriate adjustments. Not only is the removal of the board from the manufacturing process labor intensive, but depending upon the frequency of the quality control tests, hundreds of feet of insulation board could be manufactured before appropriate adjustments could be made to correct for quality control issues.
There is therefore a need to improve the manufacturing process of insulation boards such that quality control, particularly dimensional stability, can be improved.